For decades some parents, researchers and doctors have debated a possible link between autism and vaccines that contain the preservative thimerosal. Thousands of parents with autistic children took their case to court when their children developed autism after being vaccinated. But a U.S. federal court says it sees no evidence of a connection.

The court's decision came as a blow to the more than 5,000 families who say that the mercury in thimerosal caused their children's autism.

Autism spectrum disorder is a complex neurological disorder that affects a person's ability to communicate and interact with others. Treatments are often expensive.

In order to get financial compensation from the government, the families had to prove that thimerosal in vaccines caused autism in their children.

Rebecca Estepp of San Diego, has a 12 year old son with autism. She was one of the families that helped to bring the case to a special branch of federal claims court. "I was disappointed but not surprised. Vaccine court is a system where government attorneys defended a government program using government funded science, decided by government judges," she said. "I don't think these children had much of a chance."

The court released 600 pages of findings and said there is no sound evidence connecting thimerosal to autism. But the anti-vaccine groups dismissed the ruling. A national survey finds that one in four parents in the U.S. believe that vaccines containing thimerosal cause autism in healthy children and one in eight have refused at least one ecommended dose of vaccine.

That is not surprising says Arthur Allen, the author of "Vaccine," a book about vaccines and their controversies. "At some level, debates like this never really end. Like, there are still people who believe that fluoride in water is a government plot," he said.

Dr. Paul Offitt of Children's Hospital of Philadelphia says it is time to move on and find the real cause for autism. "I think today's ruling should bring comfort to parents who can finally put to rest the notion that vaccine was the problem. We can start now to focus our attention on the real cause or causes of autism, he said.

The Centers for Disease Control and Prevention reports that autism affects almost one percent of children in the U.S. Some link autism to a mother's age. Others to an autism gene. Still other research blames environmental toxins.

Inspite of several ground breaking studies on autism, there is no single treatment or cure, although experts say certain therapies and educational approaches reduce the challenges associated with the condition.